Transient amplification without population inversion in a two-field-driven ladder-type three-level system

Abstract

In this paper, the transient absorption and particle population in a two-field-driven ladder-type three energy level atomic system is simulated numerically with the density matrix equations which describe the interaction of photon and material. It is found that under the radiation of strong coupling and weak probe fields, the probe absorption shows the character of damped oscillation from the time of laser being switched on to the steady state, which presents phenomenon of full transparency. There exists negative absorption during the variation process. But most of the population is on the ground state energy level all the time. This indicates that amplification without population inversion appears during the course of transparency formation. The driving of the coupling field will produce a time-dependent coherent term. Analyzing the variation of both of the population distribution and coherent term with time, it is found that transient amplification without inversion originates from the quantum interference which is related with coupling field. Thus amplification without inversion can be obtained by controlling the intensity of laser fields and the time for laser interaction.